JPH08211518A - Radiation detector and x-ray radiographing device - Google Patents

Abstract

PURPOSE: To excellently detect X-rays in accordance with the intensity of the X-rays by performing exposure with different X-rays from an X-ray source and increasing/ decreasing the attenuation quantity of an optical attenuator in accordance with the intensity of the X-rays. CONSTITUTION: A system control part 13 gives an instruction corresponding to a fluoroscopy mode or a photographing mode to an X-ray control part 11 and a liquid crystal driving circuit 7a. When the system control part 13 gives the instruction corresponding to the fluoroscopy mode, the control part 11 applies previously set impressed voltage to an X-ray tube 3 so that the intensity of the X-rays from the X-ray tube 3 may be decreased, and the driving circuit 7a applies the previously set impressed voltage to a liquid crystal unit 7 so that the light transmissivity of the unit 7 may be increased and the attenuation quantity may be decreased. When the control part 13 gives the instruction corresponding to the photographing mode, the control part 11 applies the other previously set impressed voltage to the X-ray tube 3 so that the intensity of the X-rays from the X-ray tube 3 may be increased, and the driving circuit 7a applies the previously set impressed voltage to the unit 7 so that the light transmissivity of the unit 7 may be decreased and the attenuation quantity may be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention converts X-rays seen through a subject into electric signals and detects an X-ray transmission image of the subject to detect X-rays.
The present invention relates to an X-ray imaging device that performs line detection.

[0002]

2. Description of the Related Art Conventionally, as an X-ray photographing apparatus for detecting an X-ray transmission image of a subject, for example, a combination of a film and an intensifying screen, an image intensifier (I.
I. ) And a TV camera, and those using an imaging plate, and X-ray detection is still performed using these.

Among these, I.D. I. In the device using the, there are problems such as yarn winding distortion and shading, and a solid thin flat X-ray detector has been proposed as a solution to the problems (Demonstration of megavoltage a
nd diagnostic x-ray imaging with hydrogenated amorp
hous silicon arrays (Med Phys. 19 (6), Nov / Dec 1992;
P.1455-1466), JP-A-61-62283 "X-ray / electric conversion device", JP-A-61-244176 "digital radiographic device", etc.).

FIG. 8 is a cross-sectional view of a thin flat X-ray detector, showing a typical configuration example. Each pixel of the thin flat X-ray detector 101 has one TFT (thin film transistor) 140 and one pin photodiode (PD) 150 on a support 136, which are arranged in a matrix and are arranged above them. It has a structure having a phosphor 122. TFT140 and PD15
0 is formed of amorphous silicon by the CVD method, and glass or the like can be used as the material of the support 136. First, the pattern of the Al gate electrode 145 is formed on the support 136, and the SiN _x film 132 is formed thereon by the CVD method. SiN _x film 132
On top of this, an i-amorphous silicon (a-Si) film 14 is formed.
8, n ⁺ -amorphous silicon (n ⁺ a-Si) film 1
43 and 147 to form the channel region 1 of the TFT 140
48, the drain region and the source region of the TFT 140,
A pattern of Al drain electrode 142 and source electrode 146 is formed. On the pattern of the source electrode 146, the n ⁺ a-Si layer 154 and the i-Si layer 1 of the PD 150 are formed.
53, the p ⁺ a-Si layer 154 is formed, and the transparent electrode 126 is formed thereon. The PDs 150 are connected to each other by an Al metal electrode 125 and have a common level.

The upper part of the TFT 140 and the PD 150 is coated with a polyimide resin 124 and a transparent protective film 123, and the phosphor 122 is formed thereon. Phosphor 1
Numeral 22 absorbs X-rays and emits fluorescence corresponding to the X-ray intensity, and an optical image corresponding to the X-ray transmission image of the subject is obtained by this phosphor 122. Then, the light reflection layer 121 provided on the incident surface of the X-rays allows the fluorescence generated by the phosphor 122 to go to the PD 150 side.

X-rays incident on the detector are first converted into visible light by the phosphor and converted into electric charges by the PD 150. PD1
At 50, the charge of each pixel is accumulated according to the optical image due to the fluorescence, and the accumulated charge is read out by the switch of the TFT 140 and output as a video signal.

[0007]

The X-ray photographing apparatus has different modes for photographing a moving image and for photographing a still image, and the fluoroscopic mode for photographing a moving image is long. X-ray detection is performed by irradiating weak X-rays to irradiate time X-rays and irradiating strong X-rays in order to obtain an image with less noise in a photographing mode for photographing a still image. In the fluoroscopic mode, the weak X-rays cause a weak amount of light to enter the optical sensor, and in the imaging mode, the strong X-rays cause a strong amount of light to enter the optical sensor.

When performing X-ray detection with different X-ray intensities as described above, I.D. I. In the device using, it is possible to adjust the light quantity, open the iris to increase the light quantity when using weak X-rays, and 1/100 to 1/1 / of the weak light when using strong X-rays. The iris is narrowed down to about 1000 to suppress the amount of light and X-ray detection is performed. However, in the flat panel imager like the optical sensor made of amorphous silicon in FIG. 8, it is difficult to adjust the light amount because of its large area, and the dynamic range is insufficient with respect to the change of the X-ray intensity. Therefore, when X-ray detection using weak X-rays is enabled, the optical sensor or the like is saturated when using strong X-rays. On the contrary, when the X-ray detection using the weak X-ray is enabled, the light amount is insufficient when the strong X-ray is used, and the X-ray detection becomes difficult. As described above, there is a problem that it is difficult to perform good X-ray detection according to both modes.

The present invention has been made in view of the above circumstances, and its first object is to enable excellent X-ray detection depending on the strength of X-rays in a solid thin flat X-ray detector. Another object is to provide an X-ray imaging apparatus.

Since the thin flat X-ray detector shown in FIG. 8 has a large dynamic range,
If the amount of fluorescent light generated by the phosphor 122 is small, it will be buried in noise, making X-ray detection difficult. In order to increase the utilization efficiency of incident X-rays in order to increase the sensitivity of the detector, it is necessary to increase the thickness of the phosphor to increase the X-ray absorption rate. However, if the thickness of the phosphor is increased, light scattering inside the phosphor increases, which causes deterioration of resolution.

Therefore, a second object of the present invention is to provide a solid thin flat X-ray detector having a high sensitivity and a small deterioration of resolution, and an X-ray using this good X-ray detector. It is to provide a photographing device.

[0012]

In order to achieve the above-mentioned object, an X-ray imaging apparatus according to the invention of claim 1 of the present application is an X-ray imaging apparatus.
An X-ray imaging apparatus that detects an X-ray transmission image obtained by irradiating a subject with an X-ray transmission image as an electric signal and captures the X-ray with an X-ray source that irradiates the subject with an X-ray. Did X
An X-ray image intensifier that inputs a line transmission image from its input surface, intensifies it, and outputs it as an optical image from its output surface, and is provided on the output surface side of the X-ray image intensifier to change the light transmittance. As a result, an optical attenuator that attenuates the optical image from the output surface to a predetermined amount of light, a photodetector that converts the optical image attenuated by the optical attenuator into an electric signal, and an X-ray of different intensity from the X-ray source. And a control unit for increasing / decreasing the attenuation amount of the optical attenuator according to the intensity of the X-ray.

In the X-ray imaging apparatus according to the invention of claim 2 of the present application, in addition to the configuration of claim 1 of the application, the photodetector is a flat flat panel imager, and the photoattenuator is a liquid crystal electrode. The X-ray image intensifier has a planar structure sandwiched between and, and an optical attenuator and a photodetector are sequentially arranged close to each other on the output surface of the X-ray image intensifier.

In the radiation detector according to the invention of claim 5, a plurality of photodiodes for detecting one pixel of the X-ray image are arranged on the upper side of the support, and a signal is sequentially output from the photodiode for each pixel of the X-ray image. In a radiation detector which reads out and outputs as a video signal of an X-ray image, a first phosphor disposed between the support and the photodiode, and a second phosphor disposed above the photodiode. , Is provided.

In the radiation detector according to the invention of claim 6 of the present application, in addition to the configuration of claim 5, the first and second phosphors have a thickness of 50% to 150% of the length of one pixel. It is characterized by

According to a seventh aspect of the present invention, in addition to the structure of the fifth aspect of the present invention, the radiation detector further includes a first light reflecting film disposed below and adjacent to the first phosphor, and a second light reflecting film. And a second light reflection film disposed above the phosphor and adjacent thereto.

The radiation detector according to the invention of claim 8 is characterized in that, in addition to the configuration of claim 5, an optical fiber plate is provided between the photodiode and the first phosphor.

An X-ray imaging apparatus according to the invention of claim 9 is an X-ray imaging apparatus for detecting and photographing an X-ray transmission image obtained by irradiating an object with X-rays as an electric signal.
An X-ray source for irradiating the subject with X-rays and a plurality of photodiodes for detecting one pixel of an X-ray transmission image transmitted through the subject are arranged on the upper side of the support.
A radiation detector for sequentially reading out a signal for each pixel of a line image and outputting as a video signal of an X-ray image, the radiation detector being arranged between a support and a photodiode, and above the photodiode. And an X-ray detector including the second phosphor disposed in the above.

In the X-ray imaging apparatus according to the invention of claim 10 of the present application, in addition to the structure of claim 5, the first and second phosphors have a thickness of 50% to 150% of the length of one pixel. And the X-ray detector has a first light reflecting film disposed below and adjacent to the first phosphor and a second light reflecting film disposed adjacent to and above the second phosphor. It is characterized by including a light reflection film.

[0020]

According to the X-ray imaging apparatus of the first aspect of the present invention, the X-ray transmission image exposed from the X-ray source and transmitted through the subject is enhanced into an optical image by the X-ray imagen tensiifier. The converted optical image is attenuated by an optical attenuator having a variable light transmittance and converted into an electric signal by a photodetector. Here, since the control unit increases or decreases the attenuation amount of the optical attenuator according to the intensity of X-rays from the X-ray source, the optical image enhanced by the imagen tensiifier has an appropriate light amount by the optical attenuator. become. Since an optical image with an appropriate amount of light is converted into an electric signal by the photodetector, good X-ray detection can be performed regardless of the intensity of X-rays.

According to the X-ray imaging apparatus of the invention of claim 2, the image attenuator is configured so that the optical attenuator and the photodetector are sequentially arranged close to each other on the output surface of the X-ray image intensifier. For the optical image from the output surface of, the structure of the optical system becomes very simple.

According to the radiation detector of the fifth aspect of the present invention, the X-ray image transmitted through the second phosphor above the photodiode becomes visible light even with the first phosphor below the photodiode. Since the light is converted, the amount of light of the optical image of the X-ray image can be increased. Since the first phosphor is arranged between the support and the photodiode, the distance between the first phosphor and the photodiode becomes small, so that the deterioration of resolution is small and a highly sensitive X-ray image is obtained. Can be detected.

According to the radiation detector of the invention of claim 6, the thickness of the first and second phosphors is set to 50% to 150% of the length of one pixel, whereby the resolution is improved. Deterioration can be suppressed. Therefore, it is possible to detect a highly sensitive X-ray image with little deterioration in resolution.

According to the seventh aspect of the present invention, in the radiation detector, the first light reflection film and the second light reflection film are arranged in proximity to the first and second phosphors, whereby the fluorescence is reduced. It can be trapped by suppressing the scattering of visible light generated in the body.
Therefore, it is possible to detect an X-ray image with higher sensitivity and less deterioration in resolution.

Since the radiation detector according to the invention of claim 8 has the optical fiber plate between the photodiode and the first phosphor, deterioration of resolution can be suppressed and mechanical strength can be increased.

According to the X-ray imaging apparatus of the present invention, it is possible to detect an X-ray image with less deterioration of resolution and with higher sensitivity by virtue of the configuration using the X-ray detector. The line imaging device can be made into a simple structure.

[0027]

An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an X-ray imaging apparatus according to the first embodiment of the present invention. X-ray imaging apparatus 1 of the first embodiment
Includes an X-ray tube 3, an X-ray image intensifier (II) 5, a liquid crystal unit 7, as an X-ray optical / control system.
It has an optical sensor section 9 and an X-ray control section 11, and is provided with an input section (not shown) such as a keyboard and a system control section 13. The X-ray imaging apparatus 1 also has an A / D conversion unit 15, an image memory 17, an image processing unit 19, and D as a signal processing system for processing and displaying an analog signal of an optical image obtained by the optical sensor unit 9. The A / A converter 21 and the TV monitor 23 are provided.

The X-ray tube 3 is an X-ray source for irradiating the subject with X-rays, and the X-ray intensity thereof is the X-ray controller 11.
It changes according to the voltage from. The X-ray control unit 11 controls the X-ray exposure time and the X-ray dose of the X-ray tube 3 according to a command from the system control unit 13. X-ray I.D.
I. Numeral 5 converts an X-ray transmission image, which is emitted from the X-ray tube 3 and transmitted through the subject, into an electron image on its input surface (upper side in the figure), accelerates the electrons, and outputs it on its output side (lower side in the figure). ) Fluorescent screen enhances the optical image for conversion. This X-ray I.D. I. In the present embodiment, the reference numeral 5 is of a commonly used type having a spherical input surface and a vacuum inside.

The liquid crystal unit 7 includes an X-ray I.D. I. X-ray II. I. 5 is provided on the X-ray output surface side (on the lower side of the drawing). In the liquid crystal unit 7, the light transmittance changes according to the voltage applied from the liquid crystal drive circuit 7a, and the optical image that has passed through is attenuated according to the transmittance.

The optical sensor section 9 has an area similar to that of the liquid crystal unit 7, and is for converting an optical image from the liquid crystal unit 7 into an analog signal (charge) corresponding to the amount of light thereof. A flat panel imager including a thin flat X-ray detector 101 made of amorphous silicon is used.

FIG. 2 shows a simplified cross section of one pixel of the liquid crystal unit 7 and the photosensor section 9. X-ray I.D. I. A transparent electrode 25, a liquid crystal 27, and a lower transparent electrode 29 are arranged from the output surface side (the upper side in FIG. 2) of 5, and these constitute the liquid crystal unit 7. Liquid crystal 2
7 is sandwiched between the transparent electrode 25 and the transparent electrode 29, the light transmittance is changed by the voltage applied between the electrodes 25 and 29 from the liquid crystal drive circuit 7a provided outside, and the transmitted optical image. The amount of light can be adjusted. A polarizing filter 37 is provided below the lower transparent electrode 29,
The light passing through the liquid crystal may be polarized. Further, the polarization filter 37 may not be provided.

Below the liquid crystal unit 7, a smoothing section 3 is provided.
1, an optical sensor 33, and a field effect transistor 35 are arranged, and these constitute the optical sensor unit 9. The smoothing unit 31 includes an optical sensor 33 and a field effect transistor 35.
This is for smoothing the unevenness of, and as this material, for example, polyimide can be used. The optical sensor 33 is a photodiode of amorphous silicon that converts one pixel of the optical image into an analog signal, and is made of a PIN structure in this embodiment. The field effect transistor 35 is a MOS type made of amorphous silicon, and forms a switch for reading an analog signal from the optical sensor 33.

FIG. 3 shows a circuit configuration of the optical sensor section 9. The optical sensor 33 and the field effect transistor 35 are arranged vertically and horizontally, and the horizontal wiring connected to the gate of the field effect transistor 35 is sequentially set to a high level to sequentially turn on the transistors. The signals are sequentially read and output as a video signal.

The system control unit 13 in FIG. 1 is a controller for controlling the X-ray detection in accordance with an instruction input from the operator through the input unit, so that the X-ray detection can be performed in the fluoroscopic mode or the photographing mode. It has become. The system control unit 13 gives an instruction corresponding to the fluoroscopic mode or the imaging mode to the X-ray control unit 11 and the liquid crystal drive circuit 7a. When the system control unit 13 gives a fluoroscopic mode command, X-ray intensity from the X-ray tube 3 is reduced so that X-ray intensity decreases.
The line control unit 11 applies a predetermined applied voltage to the X-ray tube 3, and the liquid crystal drive circuit 7a operates the liquid crystal unit 7a so that the light transmittance of the liquid crystal unit 7 is large and the attenuation amount is small.
Is applied with a predetermined applied voltage. Further, when the command of the photographing mode is given, the X-ray control unit 11 gives another predetermined applied voltage to the X-ray tube 3 so that the intensity of the X-rays from the X-ray tube 3 becomes large, and the liquid crystal The drive circuit 7a is
A predetermined applied voltage is applied to the liquid crystal unit 7 so as to decrease the light transmittance of the liquid crystal unit 7 and increase the amount of attenuation.

For example, in the perspective mode, the light transmittance is 10
When the value is 0%, the voltage value is determined in advance so that the light transmittance is 1% in the photographing mode. The light transmittance is not limited to the above value, and may be 0.1% in the shooting mode, for example.

Further, this voltage value is variable by the input section, and the light transmittance can be varied even during X-ray detection. For example, the light transmittance can be changed according to the image status displayed on the TV monitor 23, and thus, the image can be adjusted to be easier to see.

The A / D conversion unit 15 is a circuit for converting the analog signal converted by the optical sensor unit 9 into a digital signal, and the image memory 17 temporarily stores the A / D converted digital signal. . Then, the image processing unit 1
Reference numeral 9 denotes a circuit for performing digital image processing such as digital subtraction on the digital signal stored in the image memory 17, and the D / A converter 21 converts the digital image-processed digital signal into an analog signal. . Then, the TV monitor 23 displays the analog signal on the screen.

Next, the operation of the X-ray imaging apparatus 1 of this embodiment will be described with reference to FIG. First, the operator inputs from the input unit of the system control unit 13 an instruction of a fluoroscopic mode in which weak X-rays are emitted for a long time during moving image observation or an imaging mode in which strong X-rays are emitted during a short time during recording. . When the system control unit 13 receives an instruction to perform the fluoroscopic mode or the imaging mode, the system control unit 13 outputs a command according to the mode to the X-ray control unit 11 and the liquid crystal drive circuit 7a.

The X-ray controller 11 sets a predetermined X-ray exposure time and X-ray dose for the X-ray tube 3 according to a command corresponding to the fluoroscopic mode or the imaging mode. On the other hand, in the liquid crystal drive circuit 7a, the voltage value applied to the upper transparent electrode 25 and the lower transparent electrode 29 is set so that the light transmittance corresponds to the transparent mode or the photographing mode.

Then, in this state, the X-ray irradiation by the X-ray tube 3 is started, and the X-ray I.D. I. In 5, the X-ray transmission image transmitted through the subject is enhanced and converted into an optical image. By passing through the liquid crystal unit 7, this enhanced optical image is appropriately attenuated and has an appropriate amount of light. For example, when the above-described transmittance is set, the optical image is attenuated to 1/100 in the photographing mode as compared with the perspective mode. However, since the X-ray intensity in the transparent mode is 1/100 of that in the imaging mode, the liquid crystal unit 7
The light amount of the optical image before passing through is 100 times greater in the photographing mode than in the perspective mode. Therefore, the amount of light of the optical image that has passed through the liquid crystal unit 7 is about the same in both the transparent mode and the photographing mode.

The optical sensor section 9 converts the optical image that has passed through the liquid crystal unit 7 into an analog video signal corresponding to the amount of light, and the A / D conversion section 15 converts the analog video signal obtained by the optical sensor section 9 into an analog video signal. After being converted into a digital signal and temporarily storing the X-ray transmission image as digital data in the image memory 17, the image processing unit 19 causes the image memory 1
Digital image processing such as digital subtraction is performed on the X-ray transmission image accumulated in 7. And
The D / A converter 21 converts the digital image processed X-ray transmission image into an analog signal, and then displays the processed X-ray transmission image on the TV monitor 23.

Thus, by increasing or decreasing the attenuation amount of the optical attenuator according to the intensity of the X-rays of the X-ray tube 3, the optical image passing through the liquid crystal unit 7 is appropriate regardless of the intensity of the X-rays. It can be the amount of light. That is, a stable image can be obtained regardless of the intensity of X-rays. Therefore, even an optical sensor unit 9 having a small dynamic range can detect a good X-ray transmission image without being saturated. Also, the liquid crystal unit 7
Since the transmittance of the optical image is not 100%, the amount of light of the optical image that has always passed is attenuated. I. It will be covered by 5 image enhancements. Therefore, even if the X-ray of the X-ray tube 3 is considerably weak, the X-ray I.D. I. With the image enhancement of 5, it becomes possible to prevent the optical sensor unit 9 having a small dynamic range from being hidden by the black level.
A good X-ray transmission image can be detected.

Further, the X-ray I.D. I. Due to the structure in which the planar optical attenuator and the optical sensor section are arranged close to the output surface of 5, the optical image from the output surface passes through the optical attenuator and is detected by the optical sensor section. As is clear from the above, the configuration of the optical system is very simple.

The present invention is not limited to the above embodiment, and various modifications can be made. For example, in the present embodiment, the light transmittance of the liquid crystal 27 of the liquid crystal unit 7 has the same value in the entire range, but the present invention is not limited to this, and the liquid crystal 27, the upper transparent electrode 25,
The lower transparent electrode 29 is formed in a plurality of regions, for example, the optical sensor unit 9
It may be divided into regions corresponding to each pixel of the optical sensor 33, and the voltage applied to the upper transparent electrode 25 and the lower transparent electrode 29 may be made variable for each region.

In this case, since the light transmittance is variable for each area, in this case, the analog signals accumulated in all the pixels of the optical sensor 33 or arbitrary pixels are monitored (for example, the analog signal from the optical sensor 33 is It is better to monitor the analog signal amount when it is output), and to lower the light transmittance of the area corresponding to the pixel when the value exceeds a preset threshold value. desirable.

By doing so, strong X-rays can be transmitted through the X-ray I.D. I. Even if the amount of light enters the optical sensor 5 and increases, the saturation of the analog signal accumulated in the optical sensor unit 9 can be prevented in that range.

Further, the optical sensor section 9 of this embodiment is made of amorphous silicon to achieve a thin and large area. However, the present invention is not limited to this, and another thin flat X-ray detector,
For example, a thin flat X-ray detector using polycrystalline silicon may be used.

Furthermore, the X-ray I.D. I. 5 can use a proximity type having a parallel plate electrode structure. The above embodiment has an advantage that the size of the optical sensor unit 9 can be made small, but has another advantage that it can be made thin when the proximity type is used.

Next, a second embodiment of the present invention will be described. FIG. 4 shows a cross section of a thin flat X-ray detector according to the second embodiment of the present invention.

A light reflecting layer 135 is first formed on a support 136 of this thin flat X-ray detector, and a phosphor 134 is formed on the light reflecting layer 135. An Al gate electrode 145 is formed on the transparent protective film formed on the phosphor 134.
Pattern is formed, and Si is formed on it by the CVD method.
The N _x film 132 is formed.

An i-amorphous silicon (a-Si) film 148 and n ⁺ -amorphous silicon (n ⁺ a-Si) films 143 and 147 are formed on the SiN _x film 132 to form a T film.
The Al drain electrode 14 is used as the channel region 148 of the FT 140, the drain region and the source region of the TFT 140.
2. A pattern of the source electrode 146 is formed to form a TFT (thin film transistor) 140 having a MOS structure. N ⁺ a-Si is formed on the pattern of the source electrode 146.
The layer 154, the i-Si layer 153, and the p ⁺ a-Si layer 154 are formed, and the transparent electrode 126 is formed thereon.
It is 0. TFT140 and PD150 are CV
It is formed of amorphous silicon by using the D method and is arranged in a matrix. 131 is a transparent electrode so that the light from the phosphor 134 can be transmitted.

FIG. 5 shows the wiring of this thin flat X-ray detector, and one TFT 140 and one PD 150 are provided for each pixel. Each PD150
Are connected to the metal electrode 125 of Al through the transparent electrode 126 and have a common level (bias level). A reading similar to a so-called CCD in which a voltage is sequentially applied to the gate of the TFT 140 from the horizontal shift register 170 to sequentially turn on, and a voltage is sequentially applied to the gate of the TFT 190 from the vertical shift register 180 to sequentially turn on. Dashi control is performed. The charge amplifier 195 amplifies the charges of the PD 150 read out pixel by pixel by this read control, and outputs the signals sequentially read out and amplified pixel by pixel of the X-ray image as a video signal. The size of one side of one pixel depends on the size of the detector, but is about 30 μm to 200 to 300 μm.
Since the metal electrode 125 is formed in a size of about m, and the width of the metal electrode 125 is at most about several μm, the PD 150 occupies most of the area of one pixel.

An upper portion of the TFT 140 and the PD 150 is coated with a polyimide resin 124 and a transparent protective film 123, and a phosphor 122 is further formed on the polyimide resin 124 and the transparent protective film 123.
The light reflection layer 1 is formed on the X-ray incidence surface on the phosphor 122.
21 is provided.

The thickness of the fluorescent material 122 above the PD 150 and the fluorescent material 134 below the PD 150 is 50 on one side of one pixel.
It is formed by 130%. In order to form the phosphors 122 and 134, a method of forming the phosphors 122 and 134 by using the same material as the intensifying screen and similarly fixing it with an adhesive, and Cs used for a scintillator
There is a method of forming I by vapor deposition. However, whichever method is used, the accuracy is not as good as the amorphous silicon forming process of the TFT 140 and the PD 150.

The phosphors 122 and 134 both have a thickness of 1
The size of one side of the pixel is best, for example, 1
If the size of one side of the pixel is 200 μm, the phosphor 12
It is desirable that each of the thicknesses of 2,134 be 200 μm. However, the thickness of the phosphors 122 and 134 should be exactly 1
Since it is impossible to make the size of one side of a pixel, by setting the phosphors 122 and 134 in the above range, the thickness thereof can be made to be about the size of one side of one pixel.
For example, if the size of one side of one pixel is 200 μm,
The thickness of the phosphors 122 and 134 is 100 to 260, respectively.
μm. When one pixel is a rectangle, the thickness of each of the phosphors 122 and 134 is determined by setting the short side as one side of one pixel.

The X-rays incident on the detector are first of all the phosphor 122.
Are converted into visible light by the phosphor 122 and PD15.
Pass 0. However, the X-rays that have passed are converted into visible light by the phosphors 122 by the phosphors 134 located below. Since the light reflecting layer 135 is provided not only on the light reflecting layer 121 on the incident surface side of the X-rays but also on the lower side of the fluorescent body 134, the fluorescent light generated by the fluorescent bodies 122 and 134 is generated by these. It will be confined in between, and most will be converted into an electric charge in PD150.

In the detector shown in the above-mentioned conventional example, it is very difficult to increase the X-ray absorption rate to 50% or more when the thickness of the phosphor is about 200 μm. On the other hand, in this embodiment,
If the X-ray absorptivities of the phosphors 122 and 134 alone are α, the X-ray absorptivities of the phosphors 122 and 134 are approximately α (2-α) by simple calculation. That is, only the phosphors 122 and 134 improve the detection efficiency by (2-α) times (> 1) as compared with the detector shown in the above-mentioned conventional example. Furthermore, the light reflection layers 121 and 135 can efficiently guide the light generated in the phosphor to the PD.

In this way, the phosphors 122 and 134 can obtain an optical image corresponding to the X-ray transmission image of the subject as a large amount of light. Since the arrangement of the phosphors 134 is between the support 136 and the PD 150, the distance between the phosphors 134 and the photodiodes 150 is small, and the deterioration of resolution is small. Further, even if light is scattered inside the phosphors 122 and 134, since the thickness is about the size of one side of one pixel, even if the light is converted into electric charges by the PD 150, it is not noticeable. Yes, deterioration of resolution is suppressed. Further, by disposing the light reflecting films 121 and 135 in close proximity to the phosphors 122 and 134, scattering of visible light generated by the phosphors is suppressed, and deterioration of resolution is suppressed.

In this way, since the PD 150 of each pixel accumulates a large electric charge and is read out to the outside due to the optical image having a larger light amount while suppressing the deterioration of resolution, the output video signal has a high sensitivity and a wide dynamic range. In addition, there is no deterioration in resolution.

As described above, with the above configuration, it is possible to obtain a thin flat X-ray detector having a high sensitivity and a large dynamic range while suppressing deterioration of resolution. Next, a third embodiment of the present invention will be described.

FIG. 6 shows a cross section of a thin flat X-ray detector according to the third embodiment of the present invention. Third above
Constituent elements that are the same as or equivalent to those in the embodiment are given the same reference numerals, and description thereof will be omitted or simplified.

The detector shown in FIG. 6 has almost the same structure as that of the third embodiment, except that an optical fiber plate 160 is provided between the transparent protective film 133 and the phosphor 134. There are features. Optical fiber plate 160
As a result, the fluorescence from the phosphor 134 is guided, so that the deterioration of the resolution is suppressed. When the optical fiber plate 160 is used, the deterioration of resolution due to the thickness is small, so that the optical fiber plate 160 can be thickened. This has the advantage of increasing mechanical strength and making the structure more robust.

Next, a fourth embodiment of the present invention will be described. FIG. 7 is a block diagram showing an X-ray imaging apparatus according to the fourth embodiment of the present invention, and the same or equivalent components as those in the first embodiment are designated by the same reference numerals.

The detector shown in FIG. I. 5, except that the liquid crystal unit 7 and the liquid crystal drive circuit 7a are substantially the same as the first embodiment, the thin flat X-ray detector according to the second embodiment is used as the optical sensor unit 9. The point is characteristic.

This X-ray imaging apparatus has an X-ray tube 3, an optical sensor section 9, and an X-ray control section 11 as an X-ray optical / control system, and an input section (not shown) such as a keyboard and system control. And a section 13. In addition, the X-ray imaging apparatus 1
An A / D converter 15, an image memory 17, an image processor 19, a D / A converter 21, and a TV monitor 23 are provided as a signal processing system for processing and displaying an analog signal of an optical image obtained by the optical sensor unit 9. I have it.

Next, the operation of the X-ray imaging apparatus of this embodiment will be described. First, the operator inputs a mode instruction from the input unit of the system control unit 13. When the system control unit 13 receives an instruction to perform the fluoroscopic mode or the imaging mode, the system control unit 13 outputs a command corresponding to the mode to the X-ray control unit 11. The X-ray control unit 11 sets a predetermined X-ray exposure time and X-ray dose for the X-ray tube 3 according to a command corresponding to the fluoroscopic mode or the imaging mode.

Then, the X-ray exposure by the X-ray tube 3 is started, and the X-ray transmission image transmitted through the subject is converted by the optical sensor section 9 into an analog video signal of an enhanced optical image.
After the analog video signal obtained by the optical sensor unit 9 is converted into a digital signal in the A / D conversion unit 15 and the X-ray transmission image is temporarily stored in the image memory 17 as digital data, in the image processing unit 19, Digital image processing such as digital subtraction is performed on the X-ray transmission image stored in the image memory 17. Then, the D / A conversion unit 21 converts the digital image processed X-ray transmission image into an analog signal, and then the processed X image on the TV monitor 23.
A line transmission image is displayed.

As is apparent from FIG. 7, the X-ray imaging apparatus of the present embodiment has a very simple structure, and since the photosensor unit 9 uses the detector of FIG. X with high sensitivity and large dynamic range while suppressing
A radiographic device can be obtained.

[0069]

As described above, according to the first aspect of the present invention, the attenuation amount of the optical attenuator increases or decreases depending on the intensity of the X-ray from the X-ray source. The intensified optical image is converted into an electric signal by the photodetector with an appropriate amount of light by the optical attenuator.
Good X-ray detection is possible regardless of the strength of the rays.

According to the second aspect of the present invention, the structure of the optical system is very simple. According to the radiation detector of the invention of claim 5, the X-ray image transmitted through the second phosphor above the photodiode is also converted into visible light by the first phosphor below the photodiode. Therefore, the light quantity of the optical image of the X-ray image can be increased. And
Since the disposition of the first phosphor is between the support and the photodiode, the distance between the first phosphor and the photodiode becomes small, so that the deterioration of resolution is small and the high sensitivity X
The line image can be detected.

According to the radiation detector of the sixth aspect of the present invention, since deterioration of resolution can be suppressed, it is possible to detect an X-ray image with less deterioration of resolution and high sensitivity. According to the radiation detector of the present invention,
By disposing the first light-reflecting film and the second light-reflecting film in close proximity to the first and second phosphors, it is possible to suppress and confine visible light generated by the phosphors. Therefore, it is possible to detect an X-ray image with higher sensitivity and less deterioration in resolution.

Since the radiation detector according to the invention of claim 8 has the optical fiber plate between the photodiode and the first phosphor, deterioration of resolution can be suppressed and mechanical strength can be increased.

According to the X-ray imaging apparatus of the present invention, it is possible to detect an X-ray image with less deterioration of resolution and higher sensitivity due to the constitution using the X-ray detector. The line imaging device can be made into a simple structure.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an X-ray imaging apparatus according to the first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a simplified cross section of a liquid crystal unit and an optical sensor section.

FIG. 3 is an explanatory diagram illustrating a circuit of an optical sensor unit.

FIG. 4 is an explanatory view showing a cross section of a thin flat X-ray detector according to the present invention.

FIG. 5 is a circuit diagram of a thin flat X-ray detector according to the present invention.

FIG. 6 is a view showing a cross section of a thin flat X-ray detector according to the present invention.

FIG. 7 is a block diagram showing an embodiment of an X-ray imaging apparatus according to the second embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a cross section of a conventional thin planar X-ray detector.

[Explanation of symbols]

1 X-ray imaging apparatus, 3 X-ray tube (X-ray source), 5 X-ray I.D. I. 7 liquid crystal unit (optical attenuator), 7a liquid crystal drive circuit, 9 optical sensor section (photodetector), 11 X-ray control section, 13 system control section, 15 A / D conversion section,
17 image memory, 19 image processing unit, 21 D /
A conversion part, 23 TV monitor, 25 upper transparent electrode, 27 liquid crystal, 29 lower transparent electrode, 31 smoothing part, 33 photosensor, 35 field effect transistor, 37 polarization filter 210 photosensor part (photodetector) 122,134 Phosphor, 123,135 light reflecting layer,
126 transparent electrode 140 TFT, 150 PD, 160 optical fiber plate

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H04N 5/32 H05G 1/64 EF

Claims (10)

[Claims] 1. X obtained by irradiating a subject with X-rays
In an X-ray imaging apparatus that detects a radiographic image as an electric signal and captures the radiographic image, an X-ray source that irradiates the subject with the X-rays, and an X-ray transmissive image that has passed through the subject from its input surface. An X-ray image intensifier which inputs and enhances and outputs as an optical image from its output surface, and an X-ray image intensifier which is provided on the output surface side of the X-ray image intensifier and which has a variable light transmittance, Attenuator for attenuating the optical image of the optical image into a predetermined amount of light, a photodetector for converting the optical image attenuated by the optical attenuator into an electric signal, and irradiating X-rays of different intensities from the X-ray source. An X-ray imaging apparatus, further comprising: a control unit that increases or decreases the amount of attenuation of the optical attenuator according to the intensity of the X-ray. 2. The photodetector is a flat-panel flat panel imager, and the photoattenuator has a flat configuration in which liquid crystal is sandwiched between electrodes, and the output of the X-ray image intensifier. The X-ray imaging apparatus according to claim 1, wherein the optical attenuator and the photodetector are sequentially arranged close to each other on a surface. 3. The optical attenuator is divided into a plurality of regions, the light transmittance is varied for each region, and the optical image is attenuated into a light image of a predetermined light amount regardless of the X-ray intensity. The X-ray imaging apparatus according to Item 1. 4. The X-ray imaging apparatus according to claim 1, wherein the photodetector has a photodetection section including amorphous silicon or polycrystalline silicon. 5. A plurality of photodiodes for detecting one pixel of the X-ray image are arranged on an upper side of a support, and a signal is sequentially read from the photodiode for each pixel of the X-ray image to obtain a signal of the X-ray image. In a radiation detector for outputting as a video signal, a first detector arranged between the support and the photodiode.
And a second phosphor arranged above the photodiode. 6. The radiation detector according to claim 5, wherein the first and second phosphors have a thickness of 50% to 150% of the length of the one pixel. 7. A first light-reflecting film that is disposed below and adjacent to the first phosphor, and a second light-reflecting film that is disposed above and above the second phosphor. The radiation detector according to claim 5, further comprising: 8. The radiation detector according to claim 5, further comprising an optical fiber plate between the photodiode and the first phosphor. 9. X obtained by irradiating a subject with X-rays
In an X-ray imaging apparatus that detects a radiographic image as an electric signal and captures the radiographic image, an X-ray source that irradiates the subject with the X-ray, and one pixel of the X-ray transmissive image that has passed through the subject. A radiation detector in which a plurality of photodiodes for detection are arranged on an upper side of a support, and a signal is sequentially read from the photodiodes for each pixel of the X-ray image and output as a video signal of the X-ray image, An X-ray detector configured to include a first phosphor disposed between the support and the photodiode, and a second phosphor disposed above the photodiode. An X-ray imaging apparatus, which is configured by: 10. The first and second phosphors are the same as the first phosphor.
The X-ray detector has a thickness of 50% to 150% of the length of a pixel, and the X-ray detector includes a first light-reflecting film disposed below and adjacent to the first phosphor. 10. The X-ray imaging apparatus according to claim 9, wherein the X-ray imaging apparatus is configured to include a second light-reflecting film that is disposed above and above the phosphor.